Antifreeze composition



Patented Dec. 12, 1950 UNITED STATES ANTIFREEZE COMPOSITION N0 Drawing. Application February 27, 1948, Serial No. 11,829

2 Claims.

This invention relates to anti-corrosive antifreeze compositions suitable for use as coolants in internal combustion engines. It also relates to processes or methods for preventing corrosion of metals which come in contact with such antifreeze compositions.

For many years it has been known that sodium tetraborate is outstandingly effective as a corrosion inhibitor in alcoholic antifreeze compositions (Kepfer, U. S. 1,911,195). have been made to provide improved antifreeze solutions containing inhibitors other than sodium tetraborate. Despite these numerous attempts, much of the antifreeze manufactured in this tetraborate corrosion inhibitor disclosed by Kepfer.

It has been discovered in recent years, however, that an improved corrosion inhibiting action by pairing sodium tetraborate with mercaptobenzothiazole (Keller, 2,373,570) or by employing an alkali metal tetraborate in combination with an alkali metal phosphate (Duus, U. S. application S. N. 337,207, filed May 25, 1940 now abandoned; Canadian Patent 438,016; Kiffer, U. S. 2,384,553). The discovery of the synergistic ac tion of the sodium tetraborate-mercaptobenzothiazole inhibitor has made possible the manufacture of antifreeze compositions which remain non-corrosive for prolonged periods of time. The pairing of an alkali metal tetraborate with an alkali metal phosphate also has given rise to antifreeze compositions superior to those obtainable by the use of individual inhibitors.

The tetraborate-phosphate inhibited antifreeze compositions, while virtually unsurpassed from the standpoint of anti-corrosion properties, have certain disadvantages, viz, when admixed with tap water available in certain cities, these mixtures yield insoluble calcium phosphate which separates out as a precipitate. The sodium tetraborate-mercaptobenzothiazole inhibited antifreeze compositions also tend to develop precipitates after prolonged use, due to the conversion of the mercaptobenzothiazole compound to relatively insoluble organic products, especially when the mixture has been subjected to the action of actinic light. The development of precipitates in alcoholic antifreeze compositions, even though not necessarily affecting the anti corrosion properties thereof is, nevertheless, highly undesirable from a practical standpoint. Small passageways in the cooling system may become blocked with solid. Also the coolant may take on a rusty ap- Many attempts pearance, which may lead to discarding the antifreeze solution more frequently than would otherwise be necessary.

An object of this invention is to provide further improvements in antifreeze compositions. A further object is to prepare a non-corrosive anti freeze composition in which the corrosion inhibitor does not tend to become converted to an insoluble precipitate under any of the conditions normally encountered in actual use. A further object is to prepare an ethylene glycol antifreeze which is superior to previously known antifreeze compositions from the standpoint of inhibition against corrosion, precipitate-formation, and

country at the present time contains the sodium foaming tendency. Other objects of the invention appear hereinafter.

It has been discovered in accordance with this invention that alkali metal metaborates are far superior to the previously employed alkali metal can be obtained by using paired inhibitors, e, g. L? tetraborates as antifreeze corrosion inhibitors.

Moreover, the alkali metal metaborates according to the invention, are efficient corrosion inhibitors in alcoholic antifreeze compositions even in the absence of added substances such as phos- Y phates which cause the development of precipitates in antifreeze compositions under conditions of actual use. In general, inhibitors which cause rapid attack on solder (e. g. inorganic nitrites, etc.) are avoided in accordance with this invention.

The alcoholic antifreeze compositions which are employed in the practice of the invention contain water-soluble alcohols, e. g. methanol, ethanol, isopropanol, ethylene glycol, propylene glycols, butylene glycols, glycerol, etc, as freezing point depressants. The preferred freezing point depressant is ethylene glycol. The watersoluble alcohols having from '1 to 3 carbon atoms per molecule are, in general, more eflicient as freezing point depressants than are alcohols of higher molecular weight.

The quantity of alkali metal metaborate employed as corrosion inhibitor should be 0.5 to 7.5% of the weight of the alcohol. Organic inhibitors, such as merc'aptobenzothiazole compounds (e. g. mercaptobenzothiazole, alkali metal mercaptobenzothiazoles, etc), di-isopropyl amine nitrite, mono-, diand triethanol amine and salts thereof, etc. may be used in combination with the alkali metal metaborate inhibitor, if desired. The weight of organic inhibitor, when one is used, should be from 0.0001 to 0.5%, based on the weight of alcohol. These organic inhibitors may be omitted altogether, if desired, or they may be used in such extremely small quantities that '3 1: any precipitate formed therefrom does not noticeably interfere with the improved results obtained through the use of the metaborate as the inorby gain in weight of the metal, was observed. The corrosion rates not thus marked represent loss of metal from the surface of the test strips.

Table I.Avoidance of formation of precipitate in antifreeze compositions [33% by volume of ethylene glycol in water] Inhibitor (weight percent based on weight of ethylene glycol) Calcium Content of Water 1 P. P. M.

Appearance of Antifreeze Source of Water Composition 2.2% borax Do. Milky-precipitate settled out.

Do. Clear.

Dayton, Galveston, Tex.

'The Ca contents. of Dayton and Marion Water, set forth above, are not unusually high.

and Lohr, average ha According to data presented by Collins, Lamar U. S. G. S. Water Supply Paper 658 (1932), theweighted rdnessof public Water'systems in 22 of the 48 States exceeds 120 (1. P. M. Ca). Table II.C'orrosion tests onmetal strips suspended in 33 volume percent ethylene glycol in water (160 F., 336 hours, stirring at 1750 R. P. M'.)

Corrosion Rate, Inches Penetration per ht b Year X Inhibitor (Weig percent ased on weight of ethylene glycol) Source of Water A1 C t 50 111111- as num Iron Copper Brass Solder 2.2% borax Marion, 0. (450 P. P. M. sulfate). 16 28 0.5 +0. 6 3 6.3% NilBOz 21120- Marion, 0 0 0 1. 5 1 O 2.7% NaBOg 2H2O .do 1 3 0.6 1.3 1 2.5% bOl'Zllx-I-O 7% sodlum phosphate 0 l 0. 7 0 1 22 Tex (300 P P M 30 '46 0.5 0.6 2

chloride). 5.0% bora Galveston, Tex 13 17 l 0 1 6.3% NaBOz.2H2O .do 1v 7 2 0.9 1 2.7% Na2BO2.2H2O 8 2 0. 9 0i 6 2.5% borax+0.70% sodium pho 3 0 0.3 0 0. 4

0.20% Na mercaptobenzothiazole Wage only (no ethylene glycol, no in- Mfar oi O. (450 P. P. M. sul- 30 145 0.5 0.5 1

i itor a e Water only (no ethylene glycol, no in- Galveston, Tex (300 P. P. M. 58 32 +1 +1 19 hibitor) chloride) ganic inhibitor. The inhibitors may be introduced into a previously used antifreeze mixture, thus providing a reinhibiting effect, if desired.

The pH of the antifreeze solution of this invention is usually within the range of 8.5 to 9.5; as measured on a water solution containing about 33% ofthe alcohol (plus inhibitor). dilute ethylene glycol solution, containing about 10% of the glycol, the pH is somewhat higher, viz. about 10. In general, the pH is within the range of 8.5 to 10. Aqueous solutions containing about 10 to of the freezing point depressant generally have a sufiiciently low melting point. Among the metals which are protected by the hereindisclosed antifreeze solutions are aluminum, iron, steel, copper, brass, solder, and the like. The most outstanding improvement in anticorrosive properties is noted when the water whichis used as the diluent 'for'the alcohol contains substantial quantities of chloride.

The'foilowing tables provide a' comparison of the antifreeze composition of this invention'with previously disclosed antifreeze compositions containing sodium tetraborate or tetraborate-phosphate inhibitors. In the figures given in the tables a plus sign indicates that an increase in the thickness of the metal test strip as measured In more Table III.C'omparison of rusting tendency and foaming tendency of antifreeze compositions (33% by volarne of ethylene glycol in water) in circulating anits'asing automobile radiators engine blocks Foaming Teng gi dency, Average Inhibitor (Weight percent raised A eared Volume Liquid on Weight of ethylene glycol) in 6% 01am Carried over in hours Foam (c. 0.).

during test 2.2% borax 520. l, 000 6.3% NaBO22H2O 1, 800 2.5% borax+0.70% sod phate+0.2% Na mercaptobenzothiazolc 1, 530 l, 900

It is believed to be apparent from the data set forth in the above tables that, in several respects, the phosphate-free metaborate-containing antifreeze'is superior to the other antifreeze compositions, which heretofore were considered to be among the best of the heretofore known antifreeze mixtures.

The term antifreeze composition as employed in the specification and claims includes the diluted antifreeze in the form in which it is circulated in the engine, and also the undiluted, or

partially diluted, form, which is suitable for packaging and shipping in accordance with the practice common in the trade. When the antifreeze composition of this invention is shipped in cans (e. g. cans made of terneplate) there is no corrosion of the metal container; even on prolonged storage the composition, as shipped, generally contains not more than about 10% by weight of water.

Since numerous modifications of the invention will occur to those who are skilled in the art, it is to be understood that I do not limit myself except as set forth in the following claims.

I claim:

1. An antifreeze composition free of phosphate and nitrite and containing from 10% to 60% by volume of ethylene glycol and from 0.5 to 7.5% by weight of alkali metal metaborate corrosion inhibitor, based on the weight of the glycol, the remainder of the composition being substantially all water, said antifreeze composition being suitable for use in an internal combustion engine cooling system.

2. An ethylene glycol anti-corrosive antifreeze composition containing from 0.5 to 7.5% by weight of sodium metaborate and a quantity of mercaptobenzothiazole compound of the class consisting of mercaptobenzothiazole and the akali metal salts thereof within the range of 0.0001 to 0.5% of the weight of the ethylene glycol, there being present no other corrosion inhibitor, said composition being characterized in that it has a pH within the range of 8.5 to 9.5 when diluted with water until the ethylene glycol content is 33%. EDWIN H. KELLER.

REFERENCES CITED The following references are of record in the file of this patent: V

UNITED STATES PATENTS Number Name Date 1,964,808 Bottoms July 3, 1934 2,386,182 Balcar Oct. 9, 1945 OTHER REFERENCES Mellors Modern Inorganic Chemistry, revised edition (1939). Longmans, Green and C0., N. Y., 

1. AN ANTIFREEZE COMPOSITION FREE OF PHOSPHATE AND NITRATE AND CONTAINING FROM 10% TO 60% BY VOLUME OF ETHYLENE GLYCOL AND FROM 0.5 TO 7.5% BY WEIGHT OF ALKALI METAL METABORATE CORROSION INHIBITOR, BASED ON THE WEIGHT OF THE GLYCOL, THE REMAINDER OF THE COMPOSITION BEING SUBSTANTIALLY ALL WATER, SAID ANTIFREEZE COMPOSITION BEING SUITABLE FOR USE IN AN INTERNAL COMBUSTION ENGINE COOLING SYSTEM. 